This application claims the priority of German patent documents 298 11 062.8, filed Jun. 23, 1998; 198 50 897.2, filed Nov. 5, 1998; 198 42 393.4, filed Sep. 16, 1998; and 198 42 394.2, filed Sep. 16, 1998 and PCT International Application No. PCT/EP99/04322, filed Jun. 22, 1999, the disclosures of which are expressly incorporated by reference herein.
The invention relates to a device for examining ocular motility.
In conventional examination techniques for detecting ocular motility disturbances (respectively, genuine or latent strabismus), the person being examined (xe2x80x9ctest personxe2x80x9d) looks simultaneously with both eyes at a white, point-shaped spot of light. At the same time a (dark) red glass is placed in front of one eye. As the so-called guide eye, this eye perceives then only the white light as a red spot of light, without surroundings. The other eye perceives the white light and the surroundings as a double image. In this manner the visual impressions of both eyes are separated.
If both eyes are not aligned correspondingly parallel, or of the light is not imaged on the corresponding retinal areas, the test person perceives subjectively the white spot of light as deviating from the red spot of light. To measure the horizontal and vertical distance between the spots of light, a display screen with a grid graduation (e.g., a so-called Harms tangent scale), is used. The center of the display screen exhibits a point-shaped white light source for the purpose of making a point-shaped spot of light available. The test person points with an optical pointer to the place on the display screen, where he perceives subjectively the red spot of light. In this manner the examining personnel can then read from the display screen the distance between the indicator""s spot of light and the central spot of fixation light and from this information derive quantitatively, e.g., the angle of squint and qualitatively with respect to convergence, divergence, or vertical difference.
In order to conduct the examination for different lines of sight, the test person normally wears a forehead lamp, which projects an indicating light on the tangent scale. The perception of double images for different lines of sight can be tested only if the head of the test person is tilted in different directions and the test person looks steadily at the central fixation light of the tangent scale. The tilt of the head is then determined by reading the indicating light on the tangent scale. If, instead of a point-shaped source of fixation light, a linear source of fixation light that can be rotated, for example, by means of a stepping motor, is used, then this examination method can be used to measure the rotational differences between both eyes. To this end, the test person receives a controller for rotating the linear source of fixation light and aligns the red and white lines of light that he perceives.
The customary examination method that is explained above is relatively space intensive, since a typically 3 mxc3x973 m tangent scale is used. Furthermore, it is also labor intensive, since examining personnel are required to read and interpret the various data from the tangent scale.
Published International patent application WO 96/13195 A1 describes a process and a device of this class for determining horizontal, vertical and/or cyclo-deviations of the eye of a test person. It also provides a device for generating an essentially point-shaped and/or linear fixation light on a board, arranged in the test person""s field of vision. The fixation light is imaged by an optical system as a virtual object point or a virtual object line at predetermined positions on the board. Furthermore, there are means to hold the head of the test person in a fixed position relative to the distance and orientation of the board. To indicate the subjective visual impression, a pointer that can be operated by the test person serves as a part of the optical projection system, which images an indicator light as a virtual object point on the board. The degree to which the test person adjusts the pointer to indicate the subjective visual impression can be measured with sensors and displayed optically and/or fed to a microprocessor.
One object of the invention is to provide a device of the type described above which can be used to examine one or several ocular motility parameter(s), with savings in space, time and personnel.
This and other objects and advantages are achieved by the ocular motility evaluation device according to the invention, which includes position sensors for adjustment and/or detection of the orientation and distance of the head of the test person in relation to the display surface and/or a sensor mechanism for detecting and determining the indicator points, representing the test person""s subjective visual impression, on the display surface. In addition, there are computerized evaluation means, to which are transmitted data about the position of the test person""s head with respect to the display surface and about the position of the indicator point on the display surface. These evaluation means evaluate this information in order to determine at least one ocular motility characteristic, such as squint angle.
As a consequence, this device significantly automates the motility examination, compared to the conventional procedure explained above. The computerized evaluation means relieve the examining individual of the corresponding evaluating tasks. The presence of the position sensor mechanism for adjustment and/or detection of the orientation and distance of the test person""s head in relation to the display surface simplifies adjustment of the test person""s head for the examining personnel; or it is possible to leave the test person""s head unfixed, detect its position with sensors and consider this information correspondingly in the evaluation means. With the presence of a sensor mechanism for determining the position of the indicator point, there is no need for the examining personnel to read the point from the display surface, to which the test person is pointing. Rather this is done automatically by the system. The device, according to the invention can use a tangent scale which is significantly smaller than the conventional dimensions, or a comparably, grid-structured display screen or also a simpler, unstructured display surface, like a simple wall.
In one embodiment of the invention, the display surface is approach sensitive (e.g., touch sensitive). For this purpose, a current so-called digitizing board can be used, for example. Then the test person can mark (with, for example, a finger or a pointer) the indicator point corresponding to his subjective visual impression, on the display surface, whose proximity sensor mechanism records this indicator information and transmits it as high resolution information about the indicator point to the computerized evaluation means. The need for reading the indicator point by the examining personnel is thus dispensed with.
Another embodiment of the invention includes a photosensitive display surface. For the display of his subjective visual impression there is for the test person a light pointer for generating a correspondingly point-shaped spot of light or a spot of light exhibiting another structure. Then the photosensor means of the display surface detects the place to which the test person aims the spot of light in accordance with his subjective visual impression, and transmits the corresponding high resolution data about the indicator point to the computerized evaluation means.
According to another feature of the invention, the indicator means may contain a mobile pointer, which can be operated by the test person. A pointer-position sensor mechanism shows the exact position (i.e., the position and orientation) of the pointer in three dimensional space as a measure for the indicator point on the display surface, to which the test person points with the pointer. In this manner the information about the indicator point can be obtained automatically from the system, without need for corresponding sensor means at the display surface.
According to still a further feature of the invention, a headlight projection unit can be fixed to the head of the test person for determining the position of the test person""s head. The headlight projection unit projects one or more spot(s) of light that indicate(s) the position of the head on a photosensitive display surface. Then its photosensor means determine the exact location of the spot of light on the display surface, indicating the position of the head, on the display surface and transmit the corresponding data on the position of the head to the computerized evaluation means. In this manner permanent fixing of the test person""s head can be dispensed with.
The latter is also possible with the device, according to another embodiment of the invention, which comprises a tracking system that is worn on the test person""s head and detects its position in three dimensional space. From this information then in the prior art arrangement of the display surface the orientation and the distance of the test person""s head can be determined automatically. Thus, with this device the position of the test person""s head can remain totally or partially unfixed, and can be detected by the system without the sensor mechanism on the side of the display surface.
In a further embodiment, the means for determining the position of the test person""s head contain an optical or ultrasound distance measuring device, with which the system automatically determines the distance and optionally also the lateral position of the test person""s head from the display surface.
Still another embodiment of the invention, includes a video camera system with related image evaluator, which finds the position of the test person""s head in space, the position of a test person-operated pointer in space, the position of a spot of indicator light, representing the subjective visual impression of the test person, and/or the position of a spot of light, which indicates the position of the head and is produced by a headlight projection unit, on the display surface.
Finally, in yet another embodiment, the computerized evaluation means contain a neural network or an expert system, known to the expert, whereby they are designed primarily for diagnostic evaluation with respect to one or several eye motility parameter(s). It is possible for the expert to implement these evaluation means by using the evaluation algorithms, which are known per se for this diagnostic purpose and which he can implement in the neural network or expert system under discussion.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.